InterDigital has violated U.S. antitrust law by failing to keep its promise to fairly license its technology considered essential to mobile phone communications, Microsoft said in a lawsuit on Thursday. The complaint against InterDigital was filed in federal court in Wilmington, Delaware.

The latest move in the long-standing fight over patent licensing between the two companies comes as the U.S. International Trade Commission is set to rule this month on whether Microsoft smartphones should be banned from being imported into the United States for infringing two of InterDigital's patents.

Microsoft alleged InterDigital's "abusive licensing practices" over its patents that are essential for companies to make cellular devices violate federal anti-monopoly laws.

A representative for InterDigital had no comment.

According to the complaint, InterDigital is also using the prospect of an import ban to coerce Microsoft into paying the price InterDigital wants for access to its technology.

In April, an ITC judge said Microsoft infringed two of InterDigital's patents related to moderating a mobile phone's power to reduce signal interference, and recommended that Microsoft's devices be blocked from import.

The full commission is scheduled to make a final ruling on the matter later this month.